How do I end/modify an endless recurring appt. without deleting past entries
or losing exceptions?

I have an appointment that occurred every Thursday from 10 am-12 noon. I set
this up in 2005 to be a recurring appointment with no end date. However, now
I'd like to delete this event as the appointment no longer occurs. If I go
to the event and "open the series" and then click on "Recurrence" and select
"Remove Recurrence," it would delete ALL entries in the series (except the
first one from 2005). If I revise the 'appointment recurrence' and set a new
'end by' date (say to yesterday), it would recreate all the entries from the
start to this end date at the same time. This isn't okay, because I had used
"Open this Occurrence" to change the time of many of those appointments or
delete occasional cancelled appointments, and all of these exceptions would
be lost if I use "Remove Recurrence" -- and I want to preserve accurate past
events.